Apparatus for the production of phthalic anhydride and benzoic acid



Sept. 10, 1935. M. SCHARFF ETAL 2,013,973

APPARATUS FOR THE PRODUCTION OF PHTHALIC ANHYDRIDE AND BENZOIC ACIDOriginal Filed Aug. 14, 1929 FRESH DECARBOXVLA T/ON FRESH CATALYSTPURlFV/NG MASS QvAPo r Inn ll In an IQQSIII SPENT CATAUST PUR/FV/NG MASSREACT/ON GASES CONTAIN/N6 PHTHAL/C ANHYD/P/DE VAPOR.

JANE/Woes. Mm SCl/HBFE ADOLF JOHANNSEN JOSEF PEICHAPT. B) WM A TTOPNEVS.

I Patented Sept. 10, 1935 UNITED STATES amass mm'rus son ma non c'rrouor PHTHALIC ANHYDRIDE ACID BENZOIG Max Scharil, Heidelberg, JohannesBrode, de-i ceased, late oi Ludwlgs Kathe hai'en-on-the-Rhine, by Brode,administratrix, Ludwigshafenon-the-Rhine, and Adolf Johannsen and JosefRelchart,

Ludwizshafen-on-the-Rhine, Germany, asslgnors to I. G. FarbenindustrleAktlengesellschaft, Frankfort-on-the-Main, Germany Original applicationAugust 14, 1929, Serial No.

385,859. Divided and this application Novemher 9, 1933, Serial No.897,302

The present invention relates to the conversion of naphthalene intophthalic anhydride by catalytic oxidation and also to the conversioninto benzoic acid of the phthalic anhydride thus ob- 5 tained without anintermediary separation and is a division of the application Ser. No.385,859, filed'August 14th, 1929, now Patent No. 1,988,876. Moreparticularly the invention relates to apparatus for purifying thephthalic anhydride, thus 10 rendering it possible toseparate it in apure state, which apparatus may also be used for the treatment of thephthalic anhydride vapors with a catalyst splitting off carbon dioxide,whereby the phthalic anhydride is converted into benzoic 15 acid.Catalysts suitable for this conversion into benzoic acid are describedand claimed in the application for patent by Johannes Brode and AdolfJohannsen, Ser. No. 149,520, filed Novem-. ber 19, 1926. The process forthe purification of 2 phthalic anhydride is generically described andclaimed in the U. S. Patent No. 1,693,915, granted December 4th, 1928,to Johannes Brode and Adolf Johannsen. A specific method of makingbenzoic acid, in which the gas mixture containing 25 phthalic anhydrideis first passed over a purifying mass or over a catalyst for makingbenzoic acid, which is poisoned and thereby reduced in its activity,forms the subject-matter of the U. S. Patent No. 1,889,945, datedDecemberfith, 1932. 30 The present invention chiefly relates toapparatus suitable forcarrying out the processes of the aforesaidpatents and application for patent.

We shall now describe our invention by reference to the production ofbenzoic acid from 35 phthalic anhydride.

While the production of phthalic anhydride by the catalytic oxidation ofnaphthalene is a highly exothermic. reaction, the conversion of thephthalic anhydride into benzoic acid proceeds 40 with only a, slightdisengagement of heat. Since the gases leaving the oxidation catalystare directly subjected to the treatment with the catalyst splitting oifcarbon dioxide, the phthalic anhydride is in a highly diluted state andthe in- 45 crease in temperature in this diluted condition is only about20 C. when the,reaction proceeds adiabatically. The most favorabletemperature for the conversion into benzoic acid is slightly lower thanthat required for the catalytic oxida- 50 tion of naphthalene and it istherefore possible to present any difficulties in practice. Means for 5controlling the temperature during the decarboxylation need not beprovided, but the gases can be brought to reaction in a simple vesselfilled with the catalyst, for example in an apparatus somewhat similarin appearance to a shaft furnace.

The conversion of the phthalic anhydride into benzoic acid is, however,attended with the difiiculty that the catalysts are very liable topoisoning by sulphuric acid vapors which are formed in the oxidation bythe combustion of organic impurities containing sulphur which arepresent in commercial naphthalene. As has been pointed out in the saidU. S. Patent No. 1,889,945 this poisoning action of the gases iscounteracted by first contacting the gases with a catalyst which hasalready been poisoned to some extent by sulphuric acid, but which isstill capable of taking up considerable amounts of sulphuric acid, andonly then contacting the gases with fresh catalyst. This process ispreferably carried out by conducting the catalyst in a counter-currentto the gases either continuouslyor periodically. In the same way highlyactive catalysts of high value can be protected by first passing thegases through masses which have a substantially lower catalytic activityand are much cheaper and which take up the sulphuric acid. Examples ofsuch purifying masses'are, for example, pumice'granules, zeolites andthe like. In such processes it is advantageous to pass at least thepurifying masses in counter-current to the gases and our inventionrelates more particularly to apparatus for conducting the catalyst orpurifying masses in counter-current to the gases in a 40 reliablemanner.

Our invention will be fully described with reference to the accompanyingdiagrammatical drawing which shows a form of apparatus suitable forcarrying out our invention.

The apparatus shown in the drawing allows of employing two differentcatalysts, or of one catalyst and a purifying mass, the gases'beingpassed first through the purifying mass and then through the catalyst.The said apparatus consists of two vertically arranged shafts and 26which may be, for example, of rectangular or square crosssectlon. Eachof the said chambers is provided with sluices 21 and 26 at the upperends and 28 and 36 at the lower ends, which serve for supplying thefresh catalyst or purifying mass and for withdrawing the spent masseswhile the apparatus is in operation. On both sides of the said chambersand also between them there are arranged narrow chambers 3|, 32, 33, 34and 35 which are connected with the shaft by the sieveplates 36, 31, 33,39, 40, 4|, 42 and 43. The gases to be treated are admitted into thechamber 3! by means of the tube 44 and pass through the sieve-plate 36into the chamber 25. They pass therethrough in horizontal direction andthen by the sieve-plate 31 into the chamber 32. From this chamber theypass through the sieve-plate 38 and again in the horizontal directionthrough the mass or catalyst in the chamber 25 and leave the chamber byway of the sieve-plate 33 and the chamber 33. They next enter thechamber 26 by way of the sieve-plate 40, pass through the mass in saidchamber again in the horizontal direction, next enter the chamber 34 byway of the sieveplate 4| and then pass through the sieve-plate 42 againinto the mass contained in the chamber 26 in the horizontal directionand are withdrawn by way of the sieve-plate 43, the chamber 35 and thetube 45. The horizontal distance between each pair of sieve-plates 36and 31, 36 and 39, 40 and 4|, 42 and 43, respectively, is smaller thanthe vertical distance between each two sieve-plates 36 and 33, 31 and36, 40 and 43, and 42, respectively, and therefore the gases pass mainlyin the horizontal direction through the catalyst or purifying mass,since this direction offers the lowest resistance to the gases. Meansmay also be provided for passing the gas leaving the chamber 36 firstthrough an annular chamber 46 surrounding the upper parts of thechambers 25 and 26, whereby the fresh catalyst or purifying mass ispreheated. In the lower part of the chambers 25 and 26, there areprovided resistance devices 41 and 48 which prevent the catalyst orpurifying mass from falling more rapidly in the center of each chamberthan at the outside thereof. when the apparatus is put into operation,it may be heated by passing through hot air, or any suitable heatingdevices may be provided in the chambers 32 and 34. a

It may be noted here that all apparatus described in the foregoing areprovided with heat insulation in order to prevent losses of heat. Thisinsulation is not shown in the drawing for the sake of greaterclearness. Also the apparatus is provided with means for controlling thetemperature which is also not shown in the drawing. In the same way ashereinbefore described for the production of benzoic acid, the apparatusmay be used for thepurification of phthalic anhydride by contact withsolid masses absorbing sulphur compounds, as for example pumice stone,silica gel, zeolites, bauxite and the like. In such case the gasesleaving the oxidation catalyst are cooled before entering thepiu'ification apparatus so far that no catalytic action of the purifyingmasses takes place. In this connection it may be pointed out that thesaid purifying masses possess to a small extent the property ofsplitting oif carbon dioxide and of producing benzoic acid when used athigh temperatures. Further the power'of the said masses of absorbingsulphuric acid is higher at lower temperatures. However, thetemperatures should not be so low that separation of the phthalicanhydride vapors contained in the gases takes place and the mostsuitable temperature is therefore about 200 C. By the separation of thesulphuric acid the formation of dark colored condensation products ofalpha-naphthoquinone during the separation of the phthalic anhydride isprevented. The small amounts of alpha-naphthoquinone present in thegases are separated only on extensive cooling together with the lasttraces of phthalic anhydride, whereas the bulk of the latter isseparated as a pure white crystalline mass or powder of excellentpurity.

What we claim is:-

1. Apparatus suitable for producing benzoic acid from phthalic anhydrideand for purifying phthalic anhydride produced by the catalytic oxidationof naphthalene which comprises two chambers, each of them having twovertical sieveplates in its lower part and two further sieveplates inits upper part and further having means for withdrawing solids from, andfor supplying fresh solids to said chamber, a gas inlet connected to oneof the lower sieves of the first chamber, a passage between the otherlower sieve and one of the upper sieves of the first chamber, a passagebetween the other upper sieve of the first chamber and one of the lowersieves of the second chamber, a passage between the other lower sieveand one of the upper sieves of the second chamber, and a gas outletconnected to the other upper sieve of the second chamber.

2. Apparatus suitable for producing benzoic acid from phthalic anhydrideand for purifying phthalic anhydride produced by the catalytic oxidationof naphthalene which comprises two chambers, each of them having twovertical sieveplates in its lower part and two further sieveplates inits upper part and further having means for withdrawing solids from, andfor supplying fresh solids to said chamber, a gas inlet connected to oneof the lower sieves of the first chamber, a passage between the otherlower sieve and one of the upper sieves of the first chamber, a passagebetween the other upper sieve of the first chamber and one of the lowersieves of the second chamber, a passage between the other lower sieveand one of the upper sieves of the second chamber, and a gas outletconnected to other upper sieve of the second chamber, the horizontaldistances between the lower and upper sieves, respectively, of onechamber being smaller than the vertical distance between correspondinglower and upper sieves.

KATHE BRODE,

Administratriz of Johannes Brode, Deceased. ADOLF J OHANNSEN. J OSEFREICHART.

